Method of manufacturing an alternator rotor

Abstract: This invention relates to an alternator rotor and its manufacturing method, said rotor having a first rotor member (1) on which a plurality of teeth (11) have been formed, plus a second rotor member (2) arranged so that its teeth are positioned in the spaces in the cylindrical surface formed by the teeth of said first rotor member. A cylindrically-shaped magnetic material (20) is cut to match the shape of the teeth (11) and is separated into a first rotor member (1) and a second rotor member (2). A plurality of teeth (11) is formed on the first rotor member (1), and teeth are formed on the second rotor member (2) so that they are positioned in the spaces in the cylindrical surface formed by the teeth of the first rotor member. The two rotor members (1,2) are mechanically joined by laying each of two rings (8,9) across the tips of the teeth (11) of one rotor member and across the bases of the teeth of the other rotor member. Given this construction and method of manufacture, rotors can be manufactured in fewer manhours, electrical efficiency can be improved by increasing the number of poles, and the incidence of defective products is decreased, which means that manufacturing yield can be increased. In addition, because the fabrication of the teeth (11) can be automated and the welding can be performed easily from the outside, fabrication precision can be increased and quality stabilized.

Description: Technical field This invention is utilized in the manufacture of alternators, and relates to auxiliary generators that are linked to the rotation of an internal combustion engine. It was developed as an alternator for automobiles, but can be utilized for other alternators as well. Prior art Combining two roundel-type poles as the rotor for an alternator is a known technology. As shown in Fig.11 (sectional view), Fig.12 (perspective view), Fig.13 (side view) and Fig.14 (perspective view), such a rotor has first rotor member 1 on which a plurality of teeth 11 have been formed, and which is fitted to rotating shaft 3. It also has second rotor member 2 which is formed in the same cylindrical surface as teeth 11 of said first rotor member 1, and in a shape that will mutually mesh with said teeth 11. Said second rotor member 2 rotates together with said first rotor member 1. Field coil 4 is arranged in the space provided between these two rotor members 1 and 2 and rotating shaft 3, and stator 5 and stator coils 6 are arranged on the outside of the two rotor members 1 and 2. Second rotor member 2 is welded to first rotor member 1 on its inside using ring 7 which is made of a non-magnetic material. Alternators with this construction have come into wide use because of the superior design which makes slip rings and brushes unnecessary, due to field coil 4 being fixed and not on the rotor side of the device. As explained above, in an alternator rotor with this sort of construction, first rotor member 1 and second rotor member 2 are manufactured separately and welded together using ring 7. This ring 7 is formed of a non-magnetic material so that it does not interfere with the lines of magnetic force that pass between teeth 11. However, this welding process has a number of drawbacks. It has to be carried out in a narrow gap, there is a large variability in product shape, and as a matter of course there is an increased proportion of defective products, so that manufacturing manhours increase. Another drawback is that expensive equipment such as laser beam welding apparatus is required. Alternator rotors with this construction have conventionally been manufactured by hot forging. Namely, first rotor member 1 and second rotor member 2 are forged separately from steel in such manner that each acquires the desired shape with a plurality of teeth 11. Such a manufacturing method therefore has the following drawbacks: large variability in product shape, increased proportion of defective products, and increased manufacturing manhours. Another method of manufacturing an alternator rotor is described in FR-A-2 347 814. The method of one of the embodiments described therein includes providing a preformed ferrous tube and then forming serrations (which in the finished rotor member form the teeth) in the tube by a series of die punching operations. In the other embodiment described therein, two identical toothed strips are cut from a single strip of magnetic material, the rotor members being then manufactured from these toothed strips. Attempts have been made to improve the efficiency of power supply units by increasing the number of teeth and thereby increasing the frequency of the alternating current generated by the alternator. However, if these teeth were formed with a smaller pitch, it would be necessary to perform the aforementioned welding process in a still narrower gap, which means that manufacturing manhours and the proportion of defective products would further increase. It is therefore difficult to increase the number of teeth beyond the number presently employed. Purposes of the invention This invention has been devised in the light of the situation described above, and its purpose is to provide an alternator rotor and a manufacturing method therefor, said rotor being capable of being welded from the outside, due to an improvement in the shape of the rings that serve to assemble the two rotor members. Another purpose of this invention is to provide an alternator rotor which is such that the proportion of defective products and the manufacturing manhours can be decreased, and the number of teeth can be made larger. Further purposes of this invention are to reduce the cost of an alternator rotor, to increase its precision, and in turn to improve the electrical efficiency of the alternator. Yet another purpose of this invention is to prevent teeth being deformed to the outside by centrifugal force during high-speed rotation: this being achieved by having the rings which ioin the two rotor members placed on the outside. Disclosure of the invention According to the invention, there is provided a method of manufacturing an alternator rotor having first and second rotor members provided with teeth, the method including a process wherein a cylindrically-shaped magnetic material is cut to match the shape of the teeth of the first rotor member characterised in that the process of cutting the cylindrically-shaped magnetic material forms two members, one of which is made into the first rotor member, and the other member is made into the second rotor member. The cylindrically-shaped magnetic material can have a shape obtained by bending one end of tube stock inwards, or it can have a cup shape in which one end is closed. It is desirable to include a process wherein a boss is joined to the aforementioned first rotor member, and a process wherein the aforementioned first rotor member and the aforementioned second rotor member are respectfully machined. That is to say, a cup shape may be formed by bending one end of tubular magnetic material, and this is then cut into shapes with a plurality of teeth which will constitute poles, after which the shapes are separated. The cutting may be carried out by a milling cutter, or by a high-density energy source such as a plasma arc or a laser beam. This makes it possible to increase the number of poles, whereby the electrical efficiency can be increased. In addition, workability in subsequent processing can be improved, variability in product quality eliminated, and yield increased. According to a further aspect of the invention the rotor that is manufactured is a rotor in which the second rotor member is so arranged that its teeth are positioned in the spaces in the cylindrical surface formed by the teeth of the first rotor member, and the method further comprises providing two rings, each of which is laid across the tips of the teeth of one of the aforementioned two rotor members and across the bases of the teeth of the other rotor member, thereby mechanically joining the two rotor members. Grooves into which the aforementioned two rings are fitted are formed in the aforementioned two rotor members, and it is desirable for these two rings to be formed from a non-magnetic material. In other words, the second rotor member is arranged so that its teeth are positioned in the spaces in the cylindrical surface of the first rotor member on which a plurality of teeth have been formed, and each of the two rings is laid across the tips of the teeth of one of the aforementioned two rotor members and across the bases of the teeth of the other rotor member, thereby mechanically joining the first rotor member and the second rotor member. The first rotor member and the second rotor member may be obtained by using a band saw to cut a single piece of material which has previously been formed into a cup shape by forging. Said material is cut into shapes with the prescribed numbers of teeth, and said shapes are then separated. As a result, a large number of teeth (i.e., of poles) can be formed. The first rotor member and the second rotor member which have thus been cut apart are fixed together by machining grooves in the tips and bases of the teeth of both rotor members, fitting two rings from both sides into the resulting grooves, and welding from the outside. Such welding is easy and the two rotor members can therefore be joined extremely easily regardless of the number of poles. Consequently, an expensive welding apparatus does not have to be used. Moreover, because the first rotor member and the second rotor member are accurately positioned by the two rings prior to welding, individual variability is small and stable quality with high precision can be maintained. Furthermore, because the number of poles can easily be increased, the electrical efficiency of the alternator can be increased by raising the frequency of the alternating current which is generated. Finally, because the rings which join the first rotor member and the second rotor member are placed on the outside, it is possible to prevent teeth being deformed to the outside by centrifugal force during high-speed rotation. Brief explanation of the drawings Fig.1 partially sectional side view showing the construction of the rotor in embodiments of this invention. Fig.2 exploded perspective view of the rotor in embodiments of this invention. Fig.3 perspective view showing the shape of the cylindrically-shaped magnetic material in a first embodiment of this invention. Fig.4 sectional view showing the shape of the cylindrically-shaped magnetic material after bending of one end in the first embodiment of this invention. Fig.5 side view showing the situation when the magnetic material in the first embodiment of this invention has been cut. Fig.6 perspective view showing the appearance and shape of the first rotor member in the first embodiment of this invention after attachment of the boss and turning. Fig.7 perspective view showing the appearance and shape of the second rotor member in the first embodiment of this invention after turning. Fig.8 partially sectional side view showing the rotor assembly in the first embodiment of this invention. Fig.9 perspective view showing the shape of the plate-shaped magnetic material in the second embodiment of this invention. Fig.10 perspective view showing the appearance of the plate-shaped magnetic material after it has been formed into a cup shape in the second embodiment of this invention. Fig.11 view showing a conventional rotor fitted to an alternator. Fig.12 perspective view showing the appearance and shape of a mounted alternator in both prior art and embodiments of this invention. Fig.13 partially sectional side view showing the construction of a conventional rotor. Fig.14 perspective view showing the construction of a conventional rotor. Explanation of symbols: 1 first rotor member 1b boss 2 second rotor member 3 rotating shaft 4 field coil 5 stator 6 stator coil 7,8,9 rings 10 groove 11 teeth 12 welds 20 cylindrically-shaped magnetic material 21 plate-shaped magnetic material 22 arrows indicating the direction of bending Embodiments Embodiments of this invention will now be explained on the basis of the drawings. Fig.1 is a partially sectional side view showing the construction of the rotor in embodiments of this invention, while Fig.2 is an exploded perspective view of the rotor in embodiments of this invention. Embodiments of this invention have first rotor member 1 on which a plurality of teeth have been formed, plus second rotor member 2 which is arranged so that its teeth 11 are positioned in the spaces in the cylindrical surface formed by teeth 11 of said first rotor member 1. Embodiments of this invention also have, as a distinguishing feature of the invention, two rings 8 and 9 made of a non-magnetic material, each of which is laid across the tips of teeth 11 of one of the aforementioned first and second rotor members 1 and 2, and across the bases of teeth 11 of the other rotor member, thereby mechanically joining the two rotor members. Embodiments of this invention also have grooves 10 which are formed for fitting the two rings 8 and 9 to first and second rotor members 1 and 2. First rotor member 1 and second rotor member 2 are obtained by using a high-density energy source such as a plasma arc or a laser to cut a single piece of material, which has previously been formed into a cup shape by forging, into shapes with a prescribed number of teeth 11, and then separating the two pieces. Grooves 10 are then machined around the outside of first rotor member 1 and second rotor member 2 at both ends. Second rotor member 2 is then arranged so that its teeth 11 are positioned in the spaces in the cylindrical surface formed by teeth 11 of first rotor member 1. Once the two rotor members have been put together in this way, they are joined mechanically by fitting ring 8 and ring 9 into respective grooves 10, said rings being fitted from the two ends of the assembly. Next, these rings 8 and 9 and first rotor member 1 and second rotor member 2 are welded from the outside at prescribed positions. Because the welding operation which joins and fixes first rotor member 1 and second rotor member 2 may be applied to the outer periphery, it is extremely easy to accomplish and can therefore be carried out reliably, and defective places will not be overlooked in an inspection. Moreover, an expensive laser beam welding apparatus is not necessary, and a substantial reduction in manufacturing cost is possible. An explanation will now be given of the method for manufacturing an alternator rotor according to embodiments of this invention. First embodiment of manufacturing method Fig.3 is a perspective view showing the shape of the cylindrically-shaped magnetic material in a first embodiment of this invention, while Fig.4 is a sectional view showing the shape of said cylindrically-shaped magnetic material after bending has been applied to one end. In this first embodiment, one end of cylindrically-shaped magnetic material 20 shown in Fig.3 is bent as shown in Fig.4 by forging or pressing. After cylindrically-shaped magnetic material 20 has been bent as shown by arrows 22, a given position on its outer periphery is mounted on a mounting jig. The mounting jig used is one which rotates and moves in the X and Y directions under numerical control. Cylindrically-shaped magnetic material 20 is then cut into shapes on which a prescribed number of teeth 11 are formed, this cutting being carried out by means of a high-density energy source such as a plasma arc or a laser. Fig.5 is a side view showing the situation after this cutting has been carried out. Fig.6 is a perspective view showing the shape of the first rotor member after these two cut shapes have been separated, and Fig.7 is a perspective view showing the shape of the second rotor member after the separation. The bent part of first rotor member 1 is turned and boss 1b fixed to it by press fitting or welding, and any required turning is carried out on the basis of this boss 1b. Any turning required for second rotor member 2 is then carried out. Fig.8 shows an example of the rotor assembly. In this example, grooves 10 have been provided in first rotor member 1 and second rotor member 2, and said rotor members have been joined by means of rings 8 and 9, and welded (at welds 12). A rotor manufactured in this way may be incorporated in the alternator shown in Fig. 11. Second embodiment of manufacturing method Fig.9 is a perspective view showing the shape of the plate-shaped magnetic material in a second embodiment of this invention, while Fig.10 is a perspective view showing the shape after said plate-shaped magnetic material has been drawn. According to the second embodiment of this invention, plate-shaped magnetic material 21 shown in Fig.9 is deep drawn by forging or pressing, and formed into the cup shape shown in Fig.10 . In other respects, this second embodiment is the same as the first embodiment. First rotor member I and second rotor member 2 of the sort shown in Fig.6 and Fig.7 can be manufactured by carrying out subsequent processing as in the first embodiment. Effect of the invention As has been explained above, according to this invention, because two rotor members can be manufactured from a single piece of material, the number of teeth constituting the poles can be increased, and the electrical efficiency of an alternator can be improved. In addition, because the separation of the two rotor members can be carried out automatically, fabrication can be carried out with high precision even when the number of teeth has been increased, and manufacturing manhours can be decreased and cost reduced. Because the welding which serves to join the first rotor member and the second rotor member can be performed from the outside, which is an easy working position, fewer manhours are involved in welding and variability in welding finish is eliminated. Because defects are not missed in inspection, high quality can be maintained. Because special welding apparatus is not required and improved product yield is obtained, manufacturing cost can be reduced. Because welding can be carried out easily even when the number of poles has been increased, the electrical efficiency of the finished product can be improved. Because the rings which mechanically join the first rotor member and the second rotor member are placed on the outside, deformation of teeth to the outside by centrifugal force during high-speed rotation can be prevented.

Claims: A method of manufacturing an alternator rotor having first and second rotor members (1,2) provided with teeth (11), the method including a process wherein a cylindrically-shaped magnetic material (20) is cut to match the shape of the teeth (11) of the first rotor member (1), characterised in that the process of cutting the cylindrically-shaped magnetic material (20) forms two members, one of which is made into the first rotor member (1), and the other member is made into the second rotor member (2). A method as claimed in claim 1, wherein the cylindrically-shaped magnetic material (20) has a shape obtained by bending one end of tube stock inwards. A method as claimed in claim 1, wherein the cylindrically-shaped magnetic material (20) has a cup shape obtained by closing one end. A method as claimed in claim 1, which includes a process of joining a boss (1b) to the aforementioned first rotor member (1). A method as claimed in any one of claims 1 to 4 which includes a process of machining the aforementioned first rotor member (1) and the aforementioned second rotor member (2), which have been obtained by the process. A method as claimed in any one of claims 1 to 5 in which the rotor that is manufactured is a rotor in which the second rotor member (2) is so arranged that its teeth (11) are positioned in the spaces in the cylindrical surface formed by the teeth (11) of the first rotor member (1), and the method further comprises providing two rings (8,9), each of which is laid across the tips of the teeth (11) of one of the aforementioned two rotor members (1,2) and across the bases of the teeth of the other rotor member, thereby mechanically joining the two rotor members. A method as claimed in claim 6, wherein grooves (10) into which the aforementioned two rings (6,9) can be fitted are formed in the aforementioned two rotor members (1,2). A method as claimed in claim 6 or 7 in which the two rings (8,9) extend around the outside of the rotor members (1,2).

Inventors: HASEGAWA KOUHEI, OTAKA HIDEKI, SAITO KENJI, HASEGAWA, KOUHEI, OTAKA, HIDEKI, SAITO, KENJI
Applicants: HINO MOTORS LTD, HINO JIDOSHA KOGYO KABUSHIKI KAISHA
Application year: 1994
Main classification: H02K1
IPC codes: H02K15, H02K1